The fossil record can give us large amounts of knowledge. But there are many other ways that the fossil record is incomplete or misleading. Scientists must keep these problems in mind when they are reading the fossil record to come to conclusions about dinosaurs and their lifestyles.
Large, heavy bones are more likely to be preserved than small, lightly built bones. So, although small vertebrates usually outnumber large, fossils of small vertebrates are scarce. This might seem to suggest that big dinosaurs dominated the landscape and that there were fewer small animals. This was probably not the case.
For dinosaur fossils to be found, the rocks where the fossils are located must be accessible. Many dinosaur-bearing formations were eroded by wind and weather long before humans were around, so their fossils have been lost forever. Other dinosaur-bearing formations are buried beneath hundreds of feet, even miles, of rock. These fossils are waiting to be excavated in the future. Only dinosaur-bearing formations that are now at the earth's surface are ready to be researched. So there is much information about the fossil record that has already been lost to erosion, but there is still much that today's paleontologists will never be able to find and evaluate.
We can also get a wrong idea about dinosaurs when scientists and paleontologists make mistakes. In the past, researchers were interested mainly in well-preserved skeletons that could be displayed in museums, so they sometimes ignored dinosaur bones unless they were new dinosaurs. Other times, they removed only the most interesting parts of the skeleton, such as the skull. They may have done this because they did not have the time or the money to excavate the whole skeleton, so they left the rest to erode.
Some museum specimens are useless because important information was recorded incorrectly or not at all. Dinosaurs have occasionally been mounted in museums with the bones in the wrong places. Museum workers have sometimes used too much plaster, restoring missing parts incorrectly. This may have mislead other researchers who relied on the published drawings and photographs of the restored skeletons. Modern methods of fossil collection and preparation have eliminated many of these problems with newly collected material. But museums have many fossils in their collections that need to be restudied.
So, everything we know about dinosaurs comes to us through an incomplete fossil record and the imperfect people who investigate it. But there is still much information that this fossil record gives us.